Jamestown Canyon virus (JCV) has been implicated as the etiologic agent of human aseptic meningitis and encephalitis only since 1982. Isolations from mosquitoes and serologic surveys have indicated that JCV has a distribution encompassing most of North America. Currently employed diagnostic procedures fail to detect virtually all human infection. When a specific and rapid diagnostic procedure is available, JCV encephalitis has the potential of being the most widely diagnosed mosquito-borne disease in the U.S. The first specific aim of this proposal is to expand the basic working description of the Midwestern cycle. The primary objectives here are to 1) identify all primary and secondary vectors, including those transmitting to humans in the late season, 2) describe these vectors' mode(s) of transmission of JCV to vertebrates, and the importance of transovarial transmission in viral amplification, dissemination, and maintenance, 3) investigate vector competence of the primary mosquito vectors, and 4) evaluate the role of bovine, cervid, and equine vertebrate hosts in viral amplification, and dissemination. The second specific aim is to develop a more complete description of the epidemiology of human infection. The primary objectives here are to 1) more clearly detail the human clinical syndrome, including prodromal symptoms and possible coinvolvement of herpes viruses in clinical illnesses, 2) identify additional major Midwestern foci of human infection such as those just recently found in suburban Chicago, IL, and the Lansing/E. Lansing, MI, areas, 3) generate computer-drawn maps delineating these foci for use in control programs, and 4) develop several ELISA procedures to provide rapid diagnosis of human illness and rapid detection of JCV antigen in arthropod tissues and vertebrate serum/blood. Standard entomological and virological methodologies including arthropod trapping and pooling, virus isolation, transmission trials, and vector competence evaluations will be employed. Serologic methodologies will include ELISA and neutralization tests in cell culture. The primary study site is in rural northcentral Michigan and has a large captive breeding deer herd that is available for long-term studies of JCV. Long-term objectives are to 1) complete the description of the natural cycle of JCV, 2) complete the elucidation of the ecology and vector competence of the primary vectors of JCV, 3) expand understanding of the epidemiology of human infection, 4) provide and ELISA for nation-wide rapid diagnosis of human infection, and 5) develop basic information that will permit the eventual control of JCV transmission and thus prevent human infection.